1. Field of the Invention
The present invention relates to a device for estimating slip angle of vehicle body, and more particularly, a device for estimating slip angle of vehicle body through cyclically repeated computer feedback calculations of related parameters.
2. Description of the Prior Art
In the vehicle stability control recently getting more popular in the art of computer based running behavior control of vehicles, the slip angle of vehicle body is one of the most desired parameters useful for effectively controlling the running behavior of vehicles. The slip angle of vehicle body is not directly detectable. It must be estimated based upon various directly detectable parameters such as steering angle, vehicle speed, lateral acceleration, yaw rate, etc. However, more essentially, the slip angle of vehicle body is dependent upon the friction coefficient between the wheel tires and the road surface which is not directly detectable, and, still worse, has a non-linearly saturating characteristic. Therefore, it was very difficult to estimate the slip angle of the vehicle body at high accuracy.
In Japanese Patent Laid-open Publication 62-83247, it is described to estimate the slip angle of vehicle body through a comparison of a slip angle of vehicle body estimated from a vehicle model inputted with input data such as steering angle and vehicle speed and a slip angle of vehicle body calculated from lateral acceleration, yaw rate and vehicle speed, while making an adjustment modification of cornering power of the front and rear wheels.
When a vehicle model is employed to estimate running behaviors of a vehicle, estimations are available generally at relatively high accuracy in a linear zone where the tire grip force against the road surface is proportional to the slip angle of wheel, but the accuracy rapidly lowers when the vehicle gets out of the linear zone according to increase of the slip angle of wheel. In the art of estimating a certain parameter by cyclically repeated computer calculations of related parameters, even a minute error of a parameter can be integrated to produce a large error which renders the estimation almost useless.